The nerve cell membrane is assumed to be involved in many important developmental events. Axon outgrowth in vivo and in vitro shows a degree of specificity which implies that the neuron has the capacity to recognize and differentiate between cell surfaces or other factors in the environment. The hypothesis of this proposal is that proteins and/or glycoproteins in the neuronal plasma membrane mediate the specific recognitions made by developing neurons. It is also hypothesized that some of the neuronal plasma membrane proteins change during development, as the neuron is confronted with new environments and new choices. The objective of the proposed research is to identify and characterize the protein and glycoprotein constituents of plasma membranes from chick embryo dorsal root ganglion neurons. Neurons will be separated from glial cells and the surface proteins of each will be labeled with 125I-lactoperoxidase or 3H-borohydride. Surface proteins will be characterized with respect to molecular weight, staining properties, and sensitivity to enzymes. Surface proteins will be compared for neurons at different stages in development. Antibodies will be made to any stage-specific proteins. This work will increase our understanding of the nerve cell membrane and its function in developmental processes. It will form a basis for future work to determine what role specific membrane proteins play in directed axon outgrowth, and may lead to the development of new clinical treatments for developmental disorders of the nervous system.